The invention refers to large area heating systems with several loops for different rooms, Large area heating systems installed in floors or ceilings, operate with low feed-line temperatures and low temperature difference between the feed-line and the return-line of a loop. Since the heating circuits in the different zones are integrated into the floor, the wall or the ceiling the thermal inertia is high, which makes the control difficult, In addition, due to the different room sizes and different distances between the pipes, the length of the loops in the different zones varies considerably.
In order to prevent that a much higher flow rate flows through a short loop due to its lower resistance than through a longer loop, releasing too much heat in the short loop, a manual control valve for each loop is placed at the manifold. These valves adjust either the resistance according to the length of the loop or in case of valves with flow meter to a calculated flow. This adjustment aims at leveling the temperature difference between the loops of different lengths, to assure that the total surface of a room to be heated especially in zones with very long loopsxe2x80x94 has the desired uniform surface temperature. In many areas, a single room control for each loop in addition to the usual boiler control is mandated by codes. Therefore, in floor- and ceiling heater systems the loop of each room has to be controlled. This requires room thermostats and an on-off valve at the manifold for each loop. As soon as the desired temperature for a room has been reached, the throughput through the loop of this room will be interrupted. The adjustment and the adaptation of each single loop to the special requirements of the room takes a lot of time and an optimal function can never be guaranteed.
Aim of the invention is to substitute the time consuming manual adjustment (which is often very inaccurate) by an automatic control unit that will maintain a constant temperature difference between the feed-line and the return-line of the loops and consequently an optimal heat distribution in the different zones.